As they say in Perl - there are many ways to get the job done.
Run TCPView from Sysinternals which will let you see what kind of connections your computer has and the processes which initiated them. If you are reasonably familiar with the processes running in your computer, you should spot any undue process accessing any outside servers.

If you have no browser/Outlook open, your residual internet activity should dwindle down to almost nothing.

This checking should be routine for a computer used for any serious activity.

It is only a beginning.